Silos have become an integral part of the industrial landscape. Whether for grain, plastic granulate, cement or animal feed, silos enable space-saving storage of bulk goods.
Of course, this often raises questions such as: How much do the contents weigh? How much of the contents are still in the silo? How much content do I use every day? Or someone wants a certain quantity to flow through within a certain period of time.
This requires a suitable scale. Weighing is usually done in kilos and tons. For particularly fine applications, also in grams or milligrams.
In the past, the contents of silos were usually measured using a level indicator. However, this is completely unreliable, suboptimal and completely outdated for Industry 4.0.
Why is a fill level indicator not enough?
If you only use the fill level as a guide, then you are only measuring the bulk material as it is poured into the silo. This can lead to several errors, which distort the measurement and sometimes cause extreme deviations.
Let's assume that you fill cement into a silo from which you remove some every day. And you always check the fill level at the beginning and end of each day.
The next few days go by without anything happening. In the evening, you check the fill level again. It appears to be enough for two more days.
But the next day, you are shocked to discover that the silo is almost empty and the little that is left is not even enough to keep operations going for a few hours.
The next regular delivery of cement will not arrive until tomorrow afternoon. To avoid a complete shutdown of operations, you make frantic phone calls and try to get hold of cement somehow.
At best, you find a dealer who sells you cement at an overpriced price. In the worst case, you can't find anyone and have to stop production for almost two days until the regular delivery arrives.
In the end, this incident costs you lost production, missed deadlines, a lot of money and a lot of nerves. You are angry about this mishap and the customers are unhappy about the delay.
But what happened?
Bulk goods do not behave like water and do not spread evenly. Rather, they form an irregular cone. Bridges or cavities can also form. If these collapse, the level measurement shows much less than on the previous day.
A high level of dust can also affect the measurement when filling the silos. Substances such as cement, lime and gypsum in particular can cause considerable fluctuations in the measurements.
For this reason, checking by reading filling levels is not very reliable and is also completely outdated nowadays.
For these reasons, measurements should be carried out using so-called load cells. However, this is usually only possible with newly built silos.
What is a load cell?
Load cells are a special type of force transducer, also known as a force sensor, which are used in the construction of weighing devices. In other words, for weighing scales. Measurements are calibrated in grams (g), kilograms (kg) and tons (t).
A distinction must be made between legal-for-trade and non-legal-for-trade load cells. Weighing cells and scales subject to mandatory verification must be checked by the verification office.
Scales and load cells subject to mandatory calibration are used, for example, in the food industry for bottling or in trade.
The EU law on metrology and verification regulates the requirements for scales and load cells and the associated electronics.
Can I have my old and larger silos retrofitted?
If you are already on the verge of a heart attack because of the impending costs, you can rest assured. There are a number of options for retrofitting old silos. And they are not expensive either.
The company Hense Wägetechnik offers so-called strain gauge strips (DMS) for measuring the weight. And without the weight being measured directly.
This is because the strips measure the electrical resistance of the outer shell of the silo. This changes under different loads, as the metal either expands or contracts.
This is recorded by the sensors. The strips are subject to the same changes as the silo when the weight changes.
Any expansion or compression changes the electrical resistance. This is measured by the strips and forwarded to a measuring module.
close-up image stain gauge sensor, retrofit silo weighing system
The strips are also insensitive to temperature fluctuations and the associated falsified measurement results. This is because the strain gage material is temperature-compensating.
You also don't have to worry about production stops when fitting the strips. The strips can be fitted during ongoing operation and it usually only takes a few hours.
The strips are also considered to be trouble-free, robust and easy to maintain. To further reduce the possibility of malfunctions, we take care of the maintenance of the strips.
We also offer various sensors for different materials such as stainless steel, aluminum and industrial steel. This is because the different materials behave physically differently and this must be adapted.
As a rule, between 2 and 8 strain gages must be fitted per silo, depending on the size and content of the silo. These are then attached to the pillars and supports using machine screws.
How should the weight of new silos be measured?
Many people still see the cost of load cells for their silos as being higher than the benefit. However, this is a myth.
As a rule, 4 load cells are installed per silo. Deviations can be detected quickly with load cells. The measurement tolerance is usually around 0.05%.
This is already an extreme improvement on normal level indicators. For these, the tolerance can be up to 33%.
However, mounting and calibrating these load cells can be difficult. If you have ever installed load cells yourself, you may be familiar with the following problems:
You've finally managed to mount the silo securely on all the load cells. Now you just need to check and calibrate the cells.
To do this, you need to check whether the individual load cells are correctly loaded. You will need a multimeter for this. You then need to disconnect the load cells, measure the signal and reconnect them.
And you have to do this a total of 4 times. Of course, this is only ideal. Realistically, fine adjustments are always required. And this is exactly where the problem lies.
If, for example, you have to reline one of the beams, you can start the calibration of all load cells again from the beginning. The values have also changed due to the modified beam.
Or the trainee may have mixed up some of the cables during installation. Cables can also break during installation. And for each of these incidents, you have to reset the load cells individually.
This costs a lot of time and nerves. Time is money and therefore such problems are unacceptable.
Hense Wägetechnik also has a suitable solution for this.
The intelligent junction box for the load cells in your silos
This box provides an overview of all load cells connected to it (the previously mentioned strain gages can also be connected to it. The individual results can be displayed in parallel.
Any faults in the cabling, cable breaks, overloads and underloads can be displayed and transmitted to the measuring amplifier. This makes monitoring during installation of the load cells and operation much easier than before.
A single intelligent junction box can keep an eye on up to 4 load cells. If there are more than 4 load cells, up to 8 of these intelligent boxes can be connected to each other via the CAN bus.
hopper scale with stainless steel load cell and intelligent junction box, application picture
If necessary, the signals are summed at the following evaluation electronics. Error messages are displayed either directly on the box or during evaluation. Fault messages and alarms can also be displayed in this way.
This intelligent box can also be installed outdoors. Like the load cells and strain gauges, it is weatherproof. The housing is made of plastic or stainless steel, depending on your requirements.
Weighing less than 700g, the boxes can be easily mounted on any pillar or wall. And without compromising the structural integrity.
The intelligent box also takes up very little space. At 174 x 120 x 37 mm and 162 x 88 x 4.5 mm for the fixings, it is relatively space-saving and can be mounted on external railings.
You don't have to worry about the visibility of the displays either. A bright, high-contrast OLED display with 256×64 pixels makes it possible to read the displays correctly in the dark as well as in difficult visibility conditions outside (fog, snowstorm).
Conclusion
Modern silos with load cells are indispensable for companies. This is because they prevent delays and production stops due to incorrectly read fill levels and the resulting miscalculations.
Existing silos can easily be retrofitted with strain gages from Hense Wägetechnik. And without interrupting production.
Whether with load cells or strain gauges, accurate silo weighing and reliable content monitoring ensure profitable work. The investment made pays for itself after just a few months.
To keep an eye on all measured values, you need innovative solutions such as the intelligent junction box from Hense Wägetechnik. You benefit from:
- A maintenance-friendly and robust design
- A bright and clearly recognizable OLED display
- Simple monitoring of all values
- Intelligent sensor technology that automatically detects overload and underload and can indicate an uneven load on the load cells
- A CAN bus interface for secure transmission of data to the evaluation module
If you have any questions or are interested in our products, please do not hesitate to contact us by phone or e-mail. We will be happy to advise you on your projects. We can also create a customized solution specifically for your needs.